[Spam?] Re: RTEMS on Zynq Microzed

Joel Sherrill joel at rtems.org
Wed Feb 17 00:19:43 UTC 2016

On Feb 16, 2016 6:17 PM, "Chris Johns" <chrisj at rtems.org> wrote:
> On 08/02/2016 06:58, Jan Sommer wrote:
>> I can confirm that compiling the BSP with BSP_ARM_A9MPCORE_PERIPHCLK set
to 333MHz fixes the timing issues.
>> After some digging I think I also found out the why (for the case
someone else stumbles upon this):
>> RTEMS registers a timer interrupt for the global timer of the Microzed's
A9 processor. It uses initialization from the arm/shared-directory because
>> global timer works similar among the A9 cores.
>> The ARM Cortex-A9 MPCore TRM section 4.3 [1] states: " The global timer
is clocked by PERIPHCLK.", which is reflected in the initialization.
>> However in Zynq-7000 TRM from Xilinx section 8.3.1 [2] they say: "The
GTC is always clocked at 1/2 of the CPU frequency (CPU_3x2x)."
>> That means the shared driver initialization sets the wrong frequency for
the Zynq-7000 family, because Xilinx deviated from the ARM reference
implementation which then breaks the computation of ticks from timespans.
>> I grepped for the BSP_ARM_A9MPCORE_PERIPHCLK-variable and corresponding
functions and it seems that it is only used in the timer initialization
routine. Therefore it should be safe to just change the variable to the
correct timer frequency without breaking other drivers which may need the
actual cpu-freqency (which is still 667 MHz in the standard setup).
> I provide the following in my init.c:
> /*
>  * Provide the peripheral clock freq.
>  */
> uint32_t a9mpcore_clock_periphclk(void)
> {
> }
> Note, the XPAR_CPU_CORTEXA9_0_CPU_CLK_FREQ_HZ name may vary depending on
your version of the Xilinx tools.
> This approach removes the need for special command line options to
configure RTEMS.

How does that work for running the tests supplied with RTEMS? Where would
this method reside then?

> Chris
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